Method and system for interference cancellation

Abstract

Systems and methods for interference cancellation at a receiver in a wireless communication system are provided. In one aspect, a method for interference cancellation is provided. The method comprises providing total received chips received from a plurality of cells. The method also comprises successively estimating received chips for each of the plurality of cells in a plurality of iterations, wherein each of the plurality of iterations after a first iteration comprises canceling previously estimated received chips for one or more of the plurality of cells from the total received chips, and estimating received chips for one of the plurality of cells using the total received chips with the previously estimated received chips for the one or more of the plurality of cells cancelled out.

What is claimed is: 
     
       1. A method for interference cancellation at a receiver in a wireless communication system, comprising:
 providing a set of total received chips associated with a plurality of users received from a plurality of cells; 
 successively estimating received chips for each of the plurality of cells in a plurality of iterations, wherein each of the plurality of iterations after a first iteration comprises: 
 removing previously estimated received chips for one or more of the plurality of cells from the set of total received chips; and 
 estimating received chips for one of the plurality of cells using the set of total received chips with the previously estimated received chips, for the one or more of the plurality of cells, removed. 
 
     
     
       2. The method of  claim 1 , wherein the successively estimating received chips for each of the plurality of cells comprises: after estimating received chips for a last cell in the plurality of cells, estimating received chips for a first cell in the plurality of cells using the set of total received chips with previously estimated received chips, for each of the plurality of cells, removed and previously estimated received chips, for the first cell, added back. 
     
     
       3. The method of  claim 2 , wherein the successively estimating received chips for each of a plurality of cells comprises: estimating received chips for a second cell in the plurality of cells using the set of total received chips with previously estimated received chips, for each of the plurality of cells, removed and previously estimated received chips, for the second cell, added back. 
     
     
       4. The method of  claim 1 , further comprising detecting a plurality of user symbols for a target cell in the plurality of cells using the set of total received chips with previously estimated received chips, for each of the plurality of cells, removed and previously estimated received chips, for the target cell, added back. 
     
     
       5. The method of  claim 1 , wherein each of the plurality of iterations comprises:
 detecting a plurality of user symbols for a working cell in the plurality of cells from a plurality of received symbols for the working cell; and 
 computing the received chips for the working cell using the plurality of detected user symbols for the working cell. 
 
     
     
       6. The method of  claim 5 , wherein detecting the plurality of user symbols for the working cell comprises:
 initially detecting the plurality of user symbols for the working cell from the plurality of received symbols for the working cell; 
 computing multi-user interference for the working cell using the initially detected plurality of user symbols for the working cell; 
 canceling the computed multi-user interference for the working cell from the plurality of received symbols for the working cell; and 
 redetecting the plurality of user symbols for the working cell from the plurality of received symbols for the working cell with the computed multi-user interference for the working cell cancelled out. 
 
     
     
       7. The method of  claim 5 , wherein computing the received chips for the working cell using the plurality of detected user symbols for the working cell comprises:
 spreading the plurality of detected user symbols for the working cell; 
 scrambling the spread plurality of detected user symbols for the working cell to obtain an estimate of transmitted chips for the working cell; and 
 applying a channel estimate to the estimate of the transmitted chips for the working cell to estimate the received chips for the working cell. 
 
     
     
       8. The method of  claim 1 , further comprising arranging the plurality of cells in an order based on signal strengths of the plurality of cells, wherein the successively computing the received chips for each of a plurality of cells is performed according to the order. 
     
     
       9. The method of  claim 8 , wherein the plurality of cells are arranged in order of decreasing signal strength. 
     
     
       10. A method for interference cancellation at a receiver in a wireless communication system, comprising:
 providing total received chips received from a plurality of cells; 
 successively estimating received chips for each of the plurality of cells in a plurality of iterations, wherein each of the plurality of iterations after a first iteration comprises:
 canceling previously estimated received chips for one or more of the plurality of cells from the total received chips; and 
 estimating received chips for one of the plurality of cells using the total received chips with the previously estimated received chips for the one or more of the plurality of cells cancelled out, 
 detecting a plurality of user symbols for a working cell in the plurality of cells from a plurality of received symbols for the working cell, wherein detecting the plurality of user symbols for the working cell comprises:
 comparing a signal strength for the working cell to a threshold; 
 if the signal strength for the working cell is equal to or above the threshold, then performing a hard slice on each of the plurality of received symbols for the working cell; and 
 if the signal strength for the working cell is below the threshold, then performing a soft slice on each of the plurality of received symbols for the working cell; and 
 
 computing the received chips for the working cell using the plurality of detected user symbols for the working cell. 
 
 
     
     
       11. A system for interference cancellation at a receiver in a wireless communication system, the system receiving a set of total received chips associated with a plurality of users received from a plurality of cells, comprising: a cell computation unit configured to successively estimate received chips for each of the plurality of cells in a plurality of iterations; and a subtraction unit, wherein in each of the plurality of iterations after a first iteration, the subtraction unit is configured to remove previously estimated received chips for one or more of the plurality of cells from the set of total received chips, and wherein in each of the plurality of iterations after the first iteration, the cell computation unit is configured to estimate received chips for one of the plurality of cells using the set of total received chips with the previously estimated received chips, for the one or more of the plurality of cells, removed. 
     
     
       12. The system of  claim 11 , wherein the cell computation unit comprises:
 a detection unit, wherein in each of the plurality of iterations, the detection unit is configured to detect a plurality of user symbols for a working cell in the plurality of cells from a plurality of received symbols for the working cell; and 
 a chip estimation unit, wherein in each of the plurality of iterations, the chip estimation unit is configured to estimate received chips for the working cell using the plurality of detected user symbols for the working cell. 
 
     
     
       13. The system of  claim 12 , wherein the detection unit comprises:
 a symbol detector; 
 an interference computation unit configured to compute multi-user interference; and 
 a subtraction unit, wherein in each of the plurality of iterations, the symbol detector is configured to initially detect the plurality of user symbols for the working cell, the interference computation unit is configured to compute multi-user interference using the initially detected plurality of user symbols for the working cell, the subtraction unit is configured to cancel the computed multi-user interference for the working cell from the plurality of received symbols for the working cell, and the symbol detector is configured to redetect the plurality of user symbols for the working cell from the plurality of received symbols for the working cell with the computed multi-user interference for the working cell cancelled out. 
 
     
     
       14. The system of  claim 12 , wherein chip estimation unit comprises:
 a spread and scramble unit configured to spread and scramble the plurality of detected user symbols for the working cell from the detection unit to obtain an estimate of transmitted user symbols for the working cell; and 
 a channel unit configured to apply a channel estimate to the estimate of the transmitted chips for the working cell to estimate the received chips for the working cell. 
 
     
     
       15. The system of  claim 11 , wherein the cell computation unit is configured to arrange the plurality of cells in an order based on signal strengths of the plurality of cells and to successively compute the received chips for each of a plurality of cells according to the order. 
     
     
       16. The system of  claim 15 , wherein the cell computation unit is configured to arrange the plurality of cells in order of decreasing signal strength. 
     
     
       17. A system for interference cancellation at a receiver in a wireless communication system, the system receiving total received chips received from a plurality of cells, comprising: a cell computation unit configured to successively estimate received chips for each of the plurality of cells in a plurality of iterations; and a subtraction unit, wherein in each of the plurality of iterations after a first iteration, the subtraction unit is configured to cancel previously estimate received chips for one or more of the plurality of cells from the total received chips; wherein in each of the plurality of iterations after the first iteration, the cell computation unit is configured to estimate received chips for one of plurality of cells using the total received chips with the previously estimated received chips for the one or more of the plurality of cells canceled out; and wherein after computing received chips for a last cell in the plurality of cells, the cell computation unit is configured to loop back to a first cell in the plurality of cells, and wherein the system further comprises: an addition unit configured to add back previously estimated received chips for the first cell to the total received chips with previously estimated received chips for each of the plurality of cells cancelled out, and wherein the cell computation unit is configured to estimate received chips for the first cell using the total received chips with the previously estimated received chips for each of the plurality of cells cancelled out and the previously estimated received chips for the first cell added back. 
     
     
       18. The system of  claim 17 , wherein the addition unit is configured to add back previously estimated received chips for a second cell in the plurality of cells to the total received chips with previously estimated received chips for each of the plurality of cells cancelled out, and wherein the cell computation unit is configured to estimate received chips for the second cell using the total received chips with the previously estimated received chips for each of the plurality of cells cancelled out and the previously estimated received chips for the second cell added back. 
     
     
       19. The system of  claim 17  further comprising:
 an addition unit configured to add back previously estimated received chips for a target cell in the plurality of cells to the total received chips with previously estimated received chips for each of the plurality of cells cancelled out; and 
 a detection unit configured to detect a plurality of user symbols for the target cell using the total received chips with the previously estimated received chips for each of the plurality of cells cancelled out and the previously estimated received chips for the target cell added back. 
 
     
     
       20. A system for interference cancellation at a receiver in a wireless communication system, the system receiving total received chips received from a plurality of cells, comprising:
 a cell computation unit configured to successively estimate received chips for each of the plurality of cells in a plurality of iterations, wherein the cell computation unit comprises:
 a detection unit, wherein in each of the plurality of iterations, the detection unit is configured to detect a plurality of user symbols for a working cell in the plurality of cells from a plurality of received symbols for the working cell, and wherein the detection unit comprises:
 a symbol detector; and 
 a selection unit configured to compare a signal strength for the working cell to a threshold and to instruct the symbol detector to perform a hard slice if the signal strength for the working cell is equal to or above the threshold and to instruct the symbol detector to perform a soft slice if the signal strength for the working cell is below the threshold; 
 
 a chip estimation unit, wherein in each of the plurality of iterations, the chip estimation unit is configured to estimate received chips for the working cell using the plurality of detected user symbols for the working cell; and 
 
 a subtraction unit, wherein in each of the plurality of iterations after a first iteration, the subtraction unit is configured to cancel previously estimated received chips for one or more of the plurality of cells from the total received chips; and wherein 
 in each of the plurality of iterations after the first iteration, the cell computation unit is configured to estimate received chips for one of plurality of cells using the total received chips with the previously estimated received chips for the one or more of the plurality of cells canceled out. 
 
     
     
       21. An apparatus for interference cancellation at a receiver in a wireless communication system, comprising: means for providing a set of total received chips associated with a plurality of users received from a plurality of cells; means for successively estimating received chips for each of the plurality of cells in a plurality of iterations, wherein for each of the plurality of iterations after a first iteration, the means for successively estimating received chips comprises: means for removing previously estimated received chips for one or more of the plurality of cells from the set of total received chips; and means for estimating received chips for one of the plurality of cells using the set of total received chips with the previously estimated received chips, for the one or more of the plurality of cells, removed. 
     
     
       22. The apparatus of  claim 21 , wherein the means for successively estimating received chips for each of the plurality of cells comprises after estimating received chips for a last cell in the plurality of cells, means for estimating received chips for a first cell in the plurality of cells using the set of total received chips with previously estimated received chips, for each of the plurality of cells, removed and previously estimated received chips, for the first cell, added back. 
     
     
       23. The apparatus of  claim 22 , wherein the means for successively estimating received chips for each of a plurality of cells comprises: means for estimating received chips for a second cell in the plurality of cells using the set of total received chips with previously estimated received chips, for each of the plurality of cells, removed and previously estimated received chips, for the second cell, added back. 
     
     
       24. The apparatus of  claim 21 , further comprising means for detecting a plurality of user symbols for a target cell in the plurality of cells using the set of total received chips with previously estimated received chips, for each of the plurality of cells, removed and previously estimated received chips, for the target cell, added back. 
     
     
       25. The apparatus of  claim 21 , wherein for each of the plurality of iterations, the means for successively estimating received chips comprises:
 means for detecting a plurality of user symbols for a working cell in the plurality of cells from a plurality of received symbols for the working cell; and 
 means for computing the received chips for the working cell using the plurality of detected user symbols for the working cell. 
 
     
     
       26. The apparatus of  claim 25 , wherein the means for detecting the plurality of user symbols for the working cell comprises:
 means for initially detecting the plurality of user symbols for the working cell from the plurality of received symbols for the working cell; 
 means for computing multi-user interference for the working cell using the initially detected plurality of user symbols for the working cell; 
 means for canceling the computed multi-user interference for the working cell from the plurality of received symbols for the working cell; and 
 means for redetecting the plurality of user symbols for the working cell from the plurality of received symbols for the working cell with the computed multi-user interference for the working cell cancelled out. 
 
     
     
       27. The apparatus of  claim 25 , wherein the means for computing the received chips for the working cell using the plurality of detected user symbols for the working cell comprises:
 means for spreading the plurality of detected user symbols for the working cell; 
 means for scrambling the spread plurality of detected user symbols for the working cell to obtain an estimate of transmitted chips for the working cell; and 
 means for applying a channel estimate to the estimate of the transmitted chips for the working cell to estimate the received chips for the working cell. 
 
     
     
       28. The apparatus of  claim 21 , further comprising means for arranging the plurality of cells in an order based on signal strengths of the plurality of cells, wherein the successively computing the received chips for each of a plurality of cells is performed according to the order. 
     
     
       29. The apparatus of  claim 28 , wherein the plurality of cells are arranged in order of decreasing signal strength. 
     
     
       30. An apparatus for interference cancellation at a receiver in a wireless communication system, comprising:
 means for providing total received chips received from a plurality of cells; 
 means for successively estimating received chips for each of the plurality of cells in a plurality of iterations, wherein for each of the plurality of iterations after a first iteration, the means for successively estimating received chips comprises:
 means for canceling previously estimated received chips for one or more of the plurality of cells from the total received chips; 
 means for estimating received chips for one of the plurality of cells using the total received chips with the previously estimated received chips for the one or more of the plurality of cells cancelled out; and 
 means for detecting a plurality of user symbols for a working cell in the plurality of cells from a plurality of received symbols for the working cell, wherein the means for detecting the plurality of user symbols for the working cell comprises:
 means for comparing a signal strength for the working cell to a threshold; 
 means for performing a hard slice on each of the plurality of received symbols for the working cell if the signal strength for the working cell is equal to or above the threshold; and 
 means for performing a soft slice on each of the plurality of received symbols for the working cell if the signal strength for the working cell is below the threshold; and 
 
 means for computing the received chips for the working cell using the plurality of detected user symbols for the working cell. 
 
 
     
     
       31. A non-transitory machine-readable medium storing instructions for interference cancellation at a receiver in a wireless communication system, the instructions comprising code for: providing a set of total received chips associated with a plurality of users received from a plurality of cells; successively estimating received chips for each of the plurality of cells in a plurality of iterations, wherein for each of the plurality of iterations after a first iteration, the code for successively estimating received chips comprises code for: removing previously estimated received chips for one or more of the plurality of cells from the set of total received chips; and estimating received chips for one of the plurality of cells using the set of total received chips with the previously estimated received chips, for the one or more of the plurality of cells, removed. 
     
     
       32. The machine-readable medium of  claim 31 , wherein the code for successively estimating received chips for each of the plurality of cells comprises code for: after estimating received chips for a last cell in the plurality of cells, estimating received chips for a first cell in the plurality of cells using the set of total received chips with previously estimated received chips, for each of the plurality of cells, removed and previously estimated received chips, for all the first cell, added back. 
     
     
       33. The machine-readable medium of  claim 32 , wherein the code for successively estimating received chips for each of a plurality of cells comprises code for: estimating received chips for a second cell in the plurality of cells using the set of total received chips with previously estimated received chips, for each of the plurality of cells, removed and previously estimated received chips, for the second cell, added back. 
     
     
       34. The machine-readable medium of  claim 31 , wherein the instructions further comprise code for detecting a plurality of user symbols for a target cell in the plurality of cells using the set of total received chips with previously estimated received chips for each of the plurality of cells removed and previously estimated received chips for the target cell added back. 
     
     
       35. The machine-readable medium of  claim 31 , wherein for each of the plurality of iterations, the code for successively estimating received chips comprises code for:
 detecting a plurality of user symbols for a working cell in the plurality of cells from a plurality of received symbols for the working cell; and 
 computing the received chips for the working cell using the plurality of detected user symbols for the working cell. 
 
     
     
       36. The machine-readable medium of  claim 35 , wherein code for detecting the plurality of user symbols for the working cell comprises code for:
 initially detecting the plurality of user symbols for the working cell from the plurality of received symbols for the working cell; 
 computing multi-user interference for the working cell using the initially detected plurality of user symbols for the working cell; 
 canceling the computed multi-user interference for the working cell from the plurality of received symbols for the working cell; and 
 redetecting the plurality of user symbols for the working cell from the plurality of received symbols for the working cell with the computed multi-user interference for the working cell cancelled out. 
 
     
     
       37. The machine-readable medium of  claim 35 , wherein the code for computing the received chips for the working cell using the plurality of detected user symbols for the working cell comprises code for:
 spreading the plurality of detected user symbols for the working cell; 
 scrambling the spread plurality of detected user symbols for the working cell to obtain an estimate of transmitted chips for the working cell; and 
 applying a channel estimate to the estimate of the transmitted chips for the working cell to estimate the received chips for the working cell. 
 
     
     
       38. The machine-readable medium of  claim 31 , wherein the instructions further comprise code for arranging the plurality of cells in an order based on signal strengths of the plurality of cells, wherein the successively computing the received chips for each of a plurality of cells is performed according to the order. 
     
     
       39. The machine-readable medium of  claim 38 , wherein the plurality of cells are arranged in order of decreasing signal strength. 
     
     
       40. A non-transitory machine-readable medium storing instructions for interference cancellation at a receiver in a wireless communication system, the instructions comprising code for:
 providing total received chips received from a plurality of cells; 
 successively estimating received chips for each of the plurality of cells in a plurality of iterations, wherein for each of the plurality of iterations after a first iteration, the code for successively estimating received chips comprises code for:
 canceling previously estimated received chips for one or more of the plurality of cells from the total received chips; 
 estimating received chips for one of the plurality of cells using the total received chips with the previously estimated received chips for the one or more of the plurality of cells cancelled out; 
 detecting a plurality of user symbols for a working cell in the plurality of cells from a plurality of received symbols for the working cell, wherein the code for detecting the plurality of user symbols for the working cell comprises code for:
 comparing a signal strength for the working cell to a threshold; 
 if the signal strength for the working cell is equal to or above the threshold, then performing a hard slice on each of the plurality of received symbols for the working cell; and 
 if the signal strength for the working cell is below the threshold, then performing a soft slice on each of the plurality of received symbols for the working cell; and 
 
 
 computing the received chips for the working cell using the plurality of detected user symbols for the working cell. 
 
     
     
       41. An apparatus for interference cancellation at a receiver in a wireless communication system, the system receiving a set of total received chips associated with a plurality of users received from a plurality of cells, comprising: at least one processor configured to successively estimate received chips for each of the plurality of cells in a plurality of iterations, wherein for each of the plurality of iterations after a first iteration, the at least one processor is configured to remove previously estimated received chips for one or more of the plurality of cells from the set of total received chips, and to estimate received chips for one of the plurality of cells using the set of total received chips with the previously estimated received chips, for the one or more of the plurality of cells, removed. 
     
     
       42. The apparatus of  claim 41 , wherein after estimating received chips for a last cell in the plurality of cells, the at least one processor is configured to estimate received chips for a first cell in the plurality of cells using the set of total received chips with previously estimated received chips, for each of the plurality of cells, removed and previously estimated received chips, for the first cell, added back. 
     
     
       43. The apparatus of  claim 42 , wherein the at least one processor is configured to estimate received chips for a second cell in the plurality of cells using the set of total received chips with previously estimated received chips, for each of the plurality of cells, removed and previously estimated received chips, for the second cell, added back. 
     
     
       44. The apparatus of  claim 41 , wherein the at least one processor is configured to detect a plurality of user symbols for a target cell in the plurality of cells using the set of total received chips with previously estimated received chips, for each of the plurality of cells, removed and previously estimated received chips for the target cell added back. 
     
     
       45. The apparatus of  claim 41 , wherein for each of the plurality of iterations, the at least one processor is configured to detect a plurality of user symbols for a working cell in the plurality of cells from a plurality of received symbols for the working cell, and to compute the received chips for the working cell using the plurality of detected user symbols for the working cell. 
     
     
       46. The apparatus of  claim 45 , wherein the at least one processor is configured to detect the plurality of user symbols for the working cell comprises by initially detecting the plurality of user symbols for the working cell from the plurality of received symbols for the working cell, computing multi-user interference for the working cell using the initially detected plurality of user symbols for the working cell, canceling the computed multi-user interference for the working cell from the plurality of received symbols for the working cell, and redetecting the plurality of user symbols for the working cell from the plurality of received symbols for the working cell with the computed multi-user interference for the working cell cancelled out. 
     
     
       47. The apparatus of  claim 45 , wherein the at least one processor is configured to compute the received chips for the working cell using the plurality of detected user symbols for the working cell by spreading the plurality of detected user symbols for the working cell, scrambling the spread plurality of detected user symbols for the working cell to obtain an estimate of transmitted chips for the working cell, and applying a channel estimate to the estimate of the transmitted chips for the working cell to estimate the received chips for the working cell. 
     
     
       48. The apparatus of  claim 41 , wherein the at least one processor is configured to arrange the plurality of cells in an order based on signal strengths of the plurality of cells, wherein the successively computing the received chips for each of a plurality of cells is performed according to the order. 
     
     
       49. The apparatus of  claim 48 , wherein the plurality of cells are arranged in order of decreasing signal strength. 
     
     
       50. An apparatus for interference cancellation at a receiver in a wireless communication system, the system receiving total received chips received from a plurality of cells, comprising:
 at least one processor configured to successively estimate received chips for each of the plurality of cells in a plurality of iterations, wherein for each of the plurality of iterations after a first iteration, the at least one processor is configured to cancel previously estimated received chips for one or more of the plurality of cells from the total received chips, to estimate received chips for one of the plurality of cells using the total received chips with the previously estimated received chips for the one or more of the plurality of cells cancelled out, to detect a plurality of user symbols for a working cell in the plurality of cells from a plurality of received symbols for the working cell, and to compute the received chips for the working cell using the plurality of detected user symbols for the working cell; 
 wherein the at least processor is configured to detect the plurality of user symbols for the working cell by comparing a signal strength for the working cell to a threshold, if the signal strength for the working cell is equal to or above the threshold, then performing a hard slice on each of the plurality of received symbols for the working cell, and if the signal strength for the working cell is below the threshold, then performing a soft slice on each of the plurality of received symbols for the working cell.